Inductive start and capacitive sustain ignition exciter system

ABSTRACT

An ignition exciter system includes an igniter, a step-up transformer, a switch device, and a spark-sustain capacitor. The igniter has a spark gap across which a spark may be generated. The step-up transformer has a primary winding that is adapted to selectively receive direct current (DC) from a DC source, and a secondary winding that is coupled to the igniter. The switch device is coupled to the primary winding and is configured to selectively operate in an ON state, in which DC may flow through the primary winding, and an OFF state, in which DC may not flow through the primary winding. The spark-sustain capacitor is coupled to the igniter and is configured to charge from a DC source when the switch device is operating in the ON state, and at least selectively discharge across the spark gap when the switch device is operating in the OFF state.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional of application Ser. No. 13/475,321, filed May 18, 2012.

TECHNICAL FIELD

The present invention generally relates to ignition exciter systems, and more particularly relates to an ignition exciter system that includes inductive start and capacitive sustain circuits.

BACKGROUND

A typical gas turbine engine includes at least a compressor section, a combustion system, and a turbine section. During operation, the compressor section draws in ambient air, compresses it, and supplies the compressed air to the combustion system. A typical combustion system includes at least a combustor, a fuel supply line, and one or more igniters. During operation, the combustion system receives fuel from a fuel source, via the fuel supply line, and the compressed air from the compressor section. The igniter(s) combusts the fuel-air mixture and supplies high energy combusted gas to the turbine section, causing it to rotate.

A combustion system igniter typically receives electrical energy from an ignition exciter system. More specifically, the ignition exciter system, in response to an ignition command supplied from an external source, such as an engine controller, supplies electrical energy to the igniter. The electrical energy supplied to the igniter is sufficient to generate a spark, which ignites the fuel-air mixture, and generates high-energy combusted gas.

Presently known ignition exciter systems are generally based on capacitive discharge ignition. In such topologies, a plurality of controlled switches, which may be connected in series or parallel, are connected in series with the energy discharge path of the spark current. These controlled switches contribute to energy loss. Thus, many of the presently known ignition exciter systems have a plurality of identical voltage balancing circuits across each of the controlled switches. Moreover, due to the poor efficiencies, many of the presently known ignition exciter systems include a relatively large storage capacitor to account for the excessive energy loss in the plurality of controlled switches. The relatively high (e.g., hundreds of amperes) discharge current that flows through the igniter may also stress the components in the discharge circuit path.

Thus, while presently known ignition exciter systems are generally safe, reliable, and robust, these systems can exhibit certain drawbacks. For example, the printed circuit board area occupied by relatively large storage capacitors and/or other components can result in relatively large enclosures, which in turn may lead to more space being occupied on the engine, can increase weight, and may result in a less efficient system.

Hence, there is a need for an ignition exciter system that uses relatively less components and/or occupies less space and/or weighs less than existing systems and/or is not relatively less efficient that existing systems. The present invention addresses one or more of these needs.

BRIEF SUMMARY

In one embodiment, an ignition exciter system includes an igniter, a step-up transformer, a switch device, and a spark-sustain capacitor. The igniter has a spark gap across which a spark may be generated. The step-up transformer has a primary winding and a secondary winding. The primary winding is adapted to selectively receive direct current (DC) from a DC source, and the secondary winding is coupled to the igniter. The switch device is coupled to the primary winding and is configured to selectively operate in an ON state, in which DC may flow through the primary winding, and an OFF state, in which DC may not flow through the primary winding. The spark-sustain capacitor is coupled to the igniter and is configured to charge from a DC source when the switch device is operating in the ON state, and at least selectively discharge across the spark gap when the switch device is operating in the OFF state.

In another embodiment, an ignition exciter system includes an igniter, a step-up transformer, a first switch device, a second switch device, and a spark-sustain capacitor.

The step-up transformer has a primary winding and a secondary winding. The primary winding is coupled to receive direct current (DC) from a DC power source, and the secondary winding is coupled to the igniter. The step-up transformer is configured to at least selectively generate a voltage at the secondary winding that is sufficient to generate a spark across the spark gap. The first switch device is coupled to the primary winding and is configured to selectively operate in an ON state, in which DC may flow through the primary winding, and an OFF state, in which DC may not flow through the primary winding. The second switch device is coupled to receive DC from a DC power source and is configured to selectively operate in an ON state and an OFF state. The spark-sustain capacitor is coupled to the second switch device and the igniter. The spark-sustain capacitor is configured to charge from a DC power source when the first and second switch devices are operating in the ON state, and at least selectively discharge across the spark gap when the first switch device is operating in the OFF state.

Furthermore, other desirable features and characteristics of the ignition exciter system will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the preceding background.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and wherein:

FIG. 1 depicts a functional block diagram of an embodiment of an ignition exciter system; and

FIG. 2 depicts a schematic diagram of one embodiment of a circuit that may be used to implement a portion of the ignition exciter system depicted in FIG. 1;

FIGS. 3-5, respectively, depict exemplary waveforms of voltage, current, and power delivered by the circuit of FIG. 2 to an igniter;

FIG. 6 depicts an exemplary waveform of current through the transformer secondary of the circuit depicted in FIG. 2;

FIG. 7 depicts a schematic diagram of another embodiment of a circuit that may be used to implement a portion of the ignition exciter system depicted in FIG. 1; and

FIG. 8 depicts a schematic diagram of yet another embodiment of a circuit that may be used to implement a portion of the ignition exciter system depicted in FIG. 1

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. As used herein, the word “exemplary” means “serving as an example, instance, or illustration.” Thus, any embodiment described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments. All of the embodiments described herein are exemplary embodiments provided to enable persons skilled in the art to make or use the invention and not to limit the scope of the invention which is defined by the claims. Furthermore, there is no intention to be bound by any expressed or implied theory presented in the preceding technical field, background, brief summary, or the following detailed description.

Referring now to FIG. 1, a functional block diagram of an embodiment of an ignition exciter system 100 is depicted and includes an igniter 102, a spark generation circuit 104, a spark sustain circuit 106, a controller 108, and an input power processing circuit 110. The igniter 102 may be any one of numerous known igniters 102 that include a spark gap 112, and that is configured, upon receipt of a sufficiently high voltage, to generate a spark across the spark gap 112. Although only a single igniter 102 is depicted, it will be appreciated that more than one igniter could be included.

The spark generation circuit 104 is coupled to the igniter 102 and is further coupled to receive commands from the controller 108. The spark generation circuit 104 is configured, in response to the commands supplied from the controller 108, to selectively generate a voltage that is sufficient to generate a spark across the spark gap 112. As will be described in more detail further below, the spark generation circuit 104 is implemented as an inductive circuit.

The spark sustain circuit 106 is coupled to the spark generation circuit 104 and is also coupled to the igniter 102. The spark sustain circuit 106 is configured to selectively supply a current to the igniter 102. More specifically, and as will be described in more detail further below, after the spark generation circuit 104 causes the igniter to generate a spark across the spark gap 112, the spark sustain circuit 106 supplies current to the igniter 102 to sustain the spark for a required time duration.

The controller 108, as noted above, is configured to supply commands to the spark generation circuit 104. The controller 108 supplies the commands to the spark generation circuit 104 to control the spark rate of the igniter 102. Though not depicted, the controller 108 may generate the commands in response to signals received from an external device, such as a non-illustrated engine controller, or the controller 108 may be implemented as part of the engine controller itself.

The input power processing circuit 110 is adapted to receive electrical power and is configured to supply DC power to the spark generation circuit 104 and the spark sustain circuit 106. The electrical power to the input power processing circuit 110 may be supplied from any one of numerous AC or DC sources. Regardless of the source of electrical power, the input power processing circuit 110 is configured to provide line, load, and temperature regulated stable DC voltages to the spark generation and spark sustain circuits 104, 106. The input power processing circuit 110 may be implemented using any known configuration of rectifiers, inverters, switched mode power supplies, batteries, passive electrical elements, electromagnetic devices, or machines, just to name a few.

A schematic diagram that depicts embodiments of the spark generation circuit 104 and the spark sustain circuit 106 is provided in FIG. 2, and will be described in detail. Before doing so, however, it is noted that the ignition exciter system 100, though not depicted in FIG. 1, may be implemented with additional functional circuit blocks. For example, the ignition exciter system 100 may include a built-in-test (BIT) circuit, one or more control power supplies, an input power processing circuit, and an input power supply, just to name a few.

Turning now to FIG. 2, the spark generation circuit 104 will first be described. This circuit includes a step-up transformer 202 and a switch device 204. The step-up transformer 202 includes a primary winding 206 and a secondary winding 208, and is configured to at least selectively generate a voltage at the secondary winding 208 that is sufficient to generate a spark across the spark gap 112. It will be appreciated that the magnitude of the voltage that is generated at the secondary winding 208 will depend upon the ratio of the number of turns in the primary winding 206 to the number of turns in the secondary winding 208, and upon the voltage magnitude connected to the primary winding 206. It will additionally be appreciated that the voltage generated at the secondary winding 208 may vary based upon, for example, the voltage needed to generate the spark.

To implement the above-described functionality, the primary winding 206 is connected, via a first resistance circuit 212, to a first DC voltage source 214, and the secondary winding 208 is connected in series with the igniter 102 and a first diode 216. The first resistance circuit 212 may be implemented using a single or multiple resistors, or using any one or more circuit elements that exhibit a desired amount of electrical resistance. The first DC voltage source 214 may be implemented using any one of numerous DC voltage generation circuits. For example, it may be implemented using any one of numerous AC/DC converters, any one of numerous DC/DC converters, or a simple battery. The first diode 216 may be implemented using a conventional diode or any one of numerous other unidirectional elements or circuits. In the depicted embodiment, however, the first diode 216 is conventional diode that includes a first anode 215 and a first cathode 217. The first anode 215 is connected to the secondary winding 208, and the first cathode 217 is connected to the igniter 102.

The switch device 204 is coupled to the primary winding 206 and is configured to selectively operate in an ON state and an OFF state. More specifically, the switch device 204 is responsive to the commands supplied from the controller 108 to operate in an ON state or an OFF state. When the switch device 204 is in the ON state, current may flow from the first DC voltage source 214 through the primary winding 206. Conversely, when the switch device 204 is in the OFF state, current will not flow through the primary winding 206. The switch device 204 may be implemented using any one of numerous types of controllable switches or switching devices. In a preferred embodiment, the switch device 204 is implemented using a solid-state device, such as a silicon-controlled rectifier (SCR), an insulated gate bipolar transistor (IGBT), a gate turn-off (GTO) thyristor, a metal-oxide semiconductor field-effect transistor (MOSFET), or an integrated gate-commutated thyristor (IGCT), just to name a few.

As FIG. 2 further depicts, the spark generation circuit 104 may optionally include a switch-protection diode 218, and an over-voltage clamp circuit 222. The switch-protection circuit 218, if included, is connected across the switch device 204. The over-voltage clamp circuit 222, if included, is connected in parallel with the primary winding 206 and includes a clamp capacitor 224, a clamp diode 226 connected in series with the clamp capacitor, and a clamp resistance circuit 228 connected in parallel with the clamp capacitor 224. The depicted over-voltage clamp circuit 222 is a passive circuit, and protects the switch device 204 in the unlikely event of an open circuit condition at the secondary winding 208. It will be appreciated that the depicted over-voltage clamp circuit 222 is merely exemplary of one type of circuit that can be used to implement this functionality, and that other circuits, both passive and active, could be used.

Turning now to the spark sustain circuit 106, it is seen that this circuit includes at least a spark-sustain capacitor 232. The spark-sustain capacitor 232 is configured to charge from a second DC voltage source 234 when the switch device 204 is operating in the ON state, and at least selectively discharge across the spark gap 112 when the switch device 204 is operating in the OFF state. To do so, the spark-sustain capacitor is coupled to the igniter 102 via a second diode 236, and is additionally coupled to the second DC voltage source 234 via a second resistance circuit 238. It will be appreciated that the second DC voltage source 234 may be implemented wholly independent of the first DC voltage source 214, or the first and second DC voltage sources 214, 234 may be implemented using a single power supply 242 (as indicated in phantom in FIG. 2). It will additionally be appreciated that spark sustain capacitor 232 may be implemented using a single or multiple capacitors that exhibit a desired amount of capacitance.

The third resistance circuit 238 may be implemented using a single or multiple resistors, or using any one or more circuit elements that exhibit a desired amount of electrical resistance. The second DC voltage source 234 may also be implemented using any one of numerous DC voltage generation circuits. For example, it may be implemented using any one of numerous AC/DC converters, any one of numerous DC/DC converters, or a simple battery. The second diode 236 may be implemented using a conventional diode or any one of numerous other unidirectional elements or circuits. In the depicted embodiment, however, the second diode 236 is conventional diode that includes a second anode 235 and a second cathode 237. The second anode 235 is connected to the spark-sustain capacitor 232, and the second cathode 237 is connected to both the igniter 102 and the first cathode 217.

Having described the structure and general function of the ignition exciter system 100, the operation of the ignition exciter system 100 will now be described. In doing so, it will be assumed that the spark generation circuit 104 and spark sustain circuit 106 are both fully discharged and/or de-energized, and that the switch device 204 is in the OFF state.

When the controller 108 commands the switch device to the ON state, DC current flows through, and magnetic energy is stored in, the primary winding 206 of the step-up transformer 202. At the same time, the spark-sustain capacitor 232 is charged, via the second resistance circuit 238, from the second DC voltage source 234. The spark-sustain capacitor 232 stores its charge until the switch device 204 is commanded to operate in the OFF state.

When the controller 108 commands the switch device 204 to the OFF state, the magnetic energy in the primary winding 206 is converted to a relatively large magnitude voltage pulse at the secondary winding 208. This relatively large magnitude voltage pulse ionizes the air in the spark gap 112, and generates a spark. This creates a low resistance discharge path for the spark-sustain capacitor 232, which discharges, via the second diode 236, through the igniter 102. As may be appreciated, the controller 108 may be configured to command the switch device 204 to switch between operating in the ON state and OFF state at an interval to generate sparks at a desired spark rate.

To even more clearly illustrate the operation of the ignition exciter system 100, reference should be made to FIGS. 3-6, which depict various waveforms of electrical parameters within the system 100. At time (t₀) the switch device 204 is in the OFF state. Thus, as depicted in FIG. 3, this causes the stored magnetic energy in step-up transformer 202 to appear as very high voltage across the spark gap 112. As a result, the air in the spark gap 112 ionizes and becomes conductive and, as depicted in FIG. 4, at the complete breakdown of the air in the spark gap 112, the spark-sustain capacitor 232 starts discharging and supplying current to sustain the spark. The electrical power delivered to the spark gap 112 is depicted in FIG. 5, and the current through the secondary winding 208 of step-up transformer 202 is depicted in FIG. 6. As may be readily apparent from FIG. 6, the step-up transformer 202 does not supply the current needed to sustain the spark in the igniter plug 102; rather, it only initiates the spark. It is the spark-sustain capacitor 232 that sustains the spark.

The spark generation circuit 104 and the spark sustain circuit 106 depicted in in FIG. 2 are merely exemplary of one embodiment for implementing these circuits, and various other circuit configurations may be used. For example, in the alternative embodiment depicted in FIG. 7, the first voltage source 214 and the second voltage source 234 are replaced with a single voltage source 702, and the spark sustain circuit 106 includes a second switch device 704. The voltage source 702 may be variously implemented and may be, for example, an AC/DC converter, a DC/DC converter, or a constant voltage power supply. The second switch 704 is connected between the third resistance circuit 238 and a node common to the spark-sustain capacitor 232 and the anode 235 of the second diode 236. The second switch device 704 disconnects the single voltage source 702 from the spark sustain circuit 106 when the spark-sustain capacitor 232 is supplying current to the spark gap 112. This further improves the efficiency of the system 100 by eliminating current flow through the third resistance circuit 238 during the sparking event. This also eliminates the potential of drawing energy from the single voltage source 702 when it is not required, which may be especially useful when the system 100 is fed from a battery.

Yet another embodiment is depicted in FIG. 8. In this embodiment, the first voltage source 214 is replaced with a constant voltage source 802, and the second voltage source 234 is replaced with a constant current source 804. The constant voltage source 802 may be variously implemented. For example, it may be implemented as an AC/DC converter, a DC/DC converter, or a constant voltage power supply. This embodiment also includes the second switch device 704, but eliminates the third resistance circuit 238, and thus its associated losses.

The ignition exciter system 100 described herein uses an inductive circuit (the spark generation circuit 104) to generate high voltage sufficient enough only to ionize the spark gap 112 and initiate a spark in an igniter 102, and a relatively low voltage capacitive circuit (the spark-sustain circuit 106) to supply the spark energy after the spark is initiated. With the described system, the spark current and spark voltage across the spark gap ascend simultaneously and thus the peak current needed to meet the peak power is significantly reduced. The described system additionally enhances efficiency, reduces part count, and thus reduces costs.

In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Numerical ordinals such as “first,” “second,” “third,” etc. simply denote different singles of a plurality and do not imply any order or sequence unless specifically defined by the claim language. The sequence of the text in any of the claims does not imply that process steps must be performed in a temporal or logical order according to such sequence unless it is specifically defined by the language of the claim. The process steps may be interchanged in any order without departing from the scope of the invention as long as such an interchange does not contradict the claim language and is not logically nonsensical.

Furthermore, depending on the context, words such as “connect” or “coupled to” used in describing a relationship between different elements do not imply that a direct physical connection must be made between these elements. For example, two elements may be connected to each other physically, electronically, logically, or in any other manner, through one or more additional elements.

While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention. It being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims. 

What is claimed is:
 1. An ignition exciter system, comprising: an igniter having a spark gap across which a spark may be generated; a step-up transformer having a primary winding and a secondary winding, the primary winding coupled to receive direct current (DC) from a DC power source, the secondary winding coupled to the igniter, the step-up transformer configured to at least selectively generate a voltage at the secondary winding that is sufficient to generate a spark across the spark gap; a first switch device coupled to the primary winding and configured to selectively operate in an ON state, in which DC may flow through the primary winding, and an OFF state, in which DC may not flow through the primary winding; a second switch device coupled to receive DC from a DC power source and configured to selectively operate in an ON state and an OFF state; and a spark-sustain capacitor coupled to the second switch device and the igniter, the spark-sustain capacitor configured to charge from a DC power source when the first and second switch devices are operating in the ON state, and at least selectively discharge across the spark gap when the first switch device is operating in the OFF state.
 2. The system of claim 1, further comprising: a controller coupled to the first and second switch devices and configured to command the first and second switch devices to selectively operate in the ON states and the OFF states.
 3. The system of claim 1, further comprising: a first diode connected between the secondary winding and the igniter and having a first anode and a first cathode, the first anode connected to the secondary winding, the first cathode connected to the igniter; and a second diode connected between the spark-sustain capacitor and the igniter and having a second anode and a second cathode, the second anode connected to the spark-sustain capacitor, the second cathode connected to the igniter and the first cathode.
 4. The system of claim 1, further comprising: a first resistance circuit connected in series with the primary winding and the first switch device; and a second resistance circuit connected between the second switch device and the second DC power source.
 5. The system of claim 1, wherein the first and second switch devices each comprise a controllable solid-state switch.
 6. The system of claim 1, further comprising: a first DC power source coupled to, and configured to supply DC to, the primary winding; and a second DC power source coupled to the second switch device, and configured to selectively charge, the spark-sustain capacitor.
 7. The system of claim 6, wherein a single power supply is configured to implement the first DC power source and the second DC power source.
 8. The system of claim 6, wherein: the first DC power source comprises a DC voltage source; and the second DC power source comprises a constant current source. 